1. Field of the Invention
The present invention relates to a preloader for use in a webbing retractor, and adapted to allow a webbing to be applied to a vehicle occupant with appropriate tightness when a vehicle suddenly decelerates.
2. Description of the Related Art
A seat belt apparatus is adapted to restrain a vehicle occupant with appropriate tightness by means of a webbing when a vehicle suddenly decelerates. If there is a large clearance between the webbing and the occupant, however, the seat belt apparatus cannot display a restraining performance sufficiently. For this reason, preloaders for allowing the webbing to be applied closely around the occupant by forcibly pulling the webbing in the direction of retraction when the vehicle suddenly decelerates, as well as webbing retractors equipped with the preloader, have been proposed.
The preloader of this type is provided with a clutch mechanism, comprised of a rotating drum, which corresponds to a takeup shaft. As a result, in a normal state of the vehicle, the preloader allows the webbing to be retracted and paid out freely without hampering the rotation of the takeup shaft. When the vehicle suddenly decelerates, however, the preloader suddenly causes the takeup shaft to rotate in a taking-up direction so as to retract the webbing immediately.
With the webbing retractor provided with such a conventional preloader, although when the vehicle suddenly decelerates, the preloader is actuated and forcibly pulls the webbing in the taking-up direction so as to apply the webbing closely around the occupant, there has been a drawback in that if a large webbing-drawing-out force acts after the webbing has been temporarily taken up (after the actuation of the preloader), the webbing is drawn out due to the so-called tight winding of the webbing in the same way as a conventional webbing retractor.
To overcome this drawback, it is conceivable to provide the preloader with a clamp member for locking the webbing so as to prevent the tight winding of the webbing. In a mechanism for preventing the tight winding of the webbing, it is necessary to provide a trigger means between a clutch mechanism and a clamp member in such a manner that the webbing is set in a state in which it is not clamped by the clamp member at normal times, while the webbing is set in a locked state by the clamp member when the vehicle suddenly decelerates. In this case, in the fabrication of the preloader, it is desired that a measure be devised so as to make it possible to render the requirement for the dimensional accuracy of the trigger means less stringent.